Abstract

Resonance enhanced multiphoton ionization and cavity ring down spectroscopies have been used to provide spatially resolved measurements of relative H atom and radical number densities, and NH column densities, in a hot filament (HF) reactor designed for diamondchemical vapor deposition and here operating with a 1% gas mixture—where n represents defined additions of or Three-dimensional modeling of the H/C/N chemistry prevailing in such HF activated gas mixtures allows the relative number densitymeasurements to be placed on an absolute scale. Experiment and theory both indicate that is largely unreactive under the prevailing experimental conditions, but additions are shown to have a major effect on the gas phase chemistry and composition. Specifically, additions introduce an additional series of “H-shift” reactions of the form which result in the formation of N atoms with calculated steady state number densities in the case of 1% additions in the hotter regions of the reactor. These react, irreversibly, with hydrocarbon species forming HCN products, thereby reducing the concentration of free hydrocarbon species (notably available to participate in diamond growth. The deduced reduction in number density due to competing gas phase chemistry is shown to be compounded by induced modifications to the hot filament surface, which reduce its efficiency as a catalyst for dissociation, thus lowering the steady state gas phase H atom concentrations and the extent and efficiency of all subsequent gas phase transformations.